Wavefront aberration compensating apparatus and ophthalmologic unit having the same

ABSTRACT

A wavefront aberration compensating apparatus, including: a deformable mirror which compensates a wavefront aberration of a light flux and includes electrodes, and a thin-film mirror which changes a configuration thereof in accordance with a voltage value applied to each of the electrodes; an optical system provided with the deformable mirror and including an object subjected to aberration compensation; a wavefront sensor which measures the wavefront aberration of the light flux; a memory which stores therein a voltage template provided for each expansion mode according to a polynomial of wavefront aberration, as a voltage alignment data for the electrodes which induces the corresponding expansion mode; and a controller configured to determine a superposition amplitude value of each of the expansion modes and calculate the voltage value applied to each of the electrodes by using the voltage templates stored such that the wavefront aberration obtained by the wavefront sensor becomes a desired aberration, and to repeat compensation of the configuration of the thin-film mirror on the basis of the calculated voltage value, such that the wavefront aberration of the light flux measured by the wavefront sensor is suppressed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is based on and claims priority from JapanesePatent Application No. 2007-065524, filed Mar. 14, 2007, the disclosureof which is hereby incorporated by reference herein in its entirety.

BACKGROUND

The present invention relates to an apparatus for compensating awavefront aberration. More specifically, the invention relates to awavefront aberration compensating apparatus for performing an aberrationcompensation which suppresses a wavefront aberration, as a factor fordetermining sharpness of an image when an object subjected to theaberration compensation, such as an eye for example, is observed,photographed and so forth at high magnification, to be small, andrelates to an ophthalmologic unit having the same.

Conventionally, there is known a retinal camera which performsobservation and photographing of a retina, by imaging the retina on thebasis of a reflected light flux from the illuminated retina. However,since the reflected light flux from the retina passes through an ocularoptical system including a cornea, a crystalline lens, a vitreous bodyfor example, the retinal camera of this kind cannot obtain an image ofthe retina at high resolution, due to an influence of an aberration inthe ocular optical system. Therefore, the conventional retinal camerahas a problem in that a sharp image of the retina cannot be obtained,even attempting to perform observation, photographing and so forth ofthe retina at high magnification. Incidentally, the ocular opticalsystem is far from an ideal optical element, possesses opticalrefractive properties which generate various aberrations such as myopiaand astigmatism, and a wavefront due to the reflected light flux fromthe retina has distortions.

On the other hand, for example, Japanese patent application publicationNo. 2005-224328 proposes an apparatus capable of obtaining a sharp imageof a retina even when a magnification is increased. The apparatusdisclosed in JP2005-224328A is provided with an aberration measurementpart which measures an optical aberration of an eye, and an aberrationcompensation part including a deformable mirror for compensatingdistortions of the wavefront of the reflected light flux caused by theoptical aberration of the eye on the basis of a signal supplied from theaberration measurement part.

In a conventional technology, plural kinds of voltage variationtemplates such as a concentric template, a symmetrical template and anasymmetrical template are provided for adjusting a deformable mirrorwhen a wavefront aberration is to be compensated by using the deformablemirror. The voltage variation templates are selected on the basis of themeasured wavefront aberration, and one of voltage patterns as voltagevalues for respective electrodes is determined from the selected voltagevariation template. The determination of the voltage patterns isrepeated to perform the compensation of the wavefront aberration inwhich the deformable mirror is used.

Generally, an arithmetic processing method for the compensation of thewavefront aberration, in which the templates are utilized, includes adistortion, generated when a voltage is applied to a single electrode,as an influence function. The influence functions corresponding to therespective electrodes are superposed to calculate voltage alignment datacorresponding to an objective configuration of the deformable mirror.Hence, since a unit of the templates is equivalent to the number ofelectrodes, an amount of calculation increases depending upon the numberof electrodes.

Additionally, in the conventional technology in which three kinds oftemplates are provided, a congruence of the wavefront aberration to eachexpansion mode subjected to the compensation cannot be obtained by thetemplates of three kinds. Also, it is necessary to use the arithmeticprocessing method for the wavefront aberration compensation, in whichthe distortion generated when the voltage is applied to thepredetermined electrode is included as the influence function, and tocalculate a superposition coefficient used when the influence functionscorresponding to the respective electrodes are superposed. Thecalculation for the superposition coefficients, however, requires time.Therefore, it is often said that the arithmetic processing method forthe compensation of the wavefront aberration, in which the templates areused, is normally not suitable for the deformable mirror having thelarge number of electrodes.

Furthermore, the number of times of repetition of the compensation bythe voltage patterns decreases when a target value for a residualaberration, as a difference between a wavefront aberration of an eye forexample and an aberration compensated by the deformable mirror, is setto be large. Thus, the time required, for example, in photographing of aretina from initiation of the photographing to finishing of thephotographing is shortened. However, a sharp image cannot bephotographed when a high magnification is set.

In contrast, the sharp image is obtainable even when the highmagnification is set, when the target value for the residual aberrationis set to be small. However, the number of times for the repeatedcompensation by the voltage patterns is increased, and thus, the timerequired, for example, in the photographing of the retina from theinitiation of the photographing to the finishing of the photographingbecomes long.

Here, reasons why the control of compensating the deformable mirror isrepeatedly performed by the voltage patterns, such that a shape of athin-film mirror of the deformable mirror becomes nearer to theobjective configuration, will be described.

The deformable mirror includes plural electrodes arranged at apredetermined interval on a back face of the thin-film mirror, and avoltage is applied to each of the electrodes, to deform the thin-filmmirror only by a pulling force or an electrostatic force. In addition,since the thin-film mirror of the deformable mirror is a continuum, therespective electrodes cannot be treated individually for the shapedeformation of the thin-film mirror. Hence, when one point of thethin-film mirror is pulled by one electrode, a part of the thin-filmmirror corresponding to that one electrode is deformed largely, and atthe same time, a part of the thin-film mirror corresponding to otherelectrodes is also deformed. Therefore, the compensation control of thedeformable mirror is performed repeatedly by the voltage patterns, sincethe entire surface of the mirror is influenced when one part of thethin-film mirror is pulled.

Secondly, when a retina of an eye is to be photographed for example, aduration time in which a person can keep its eye open with goodcondition is several seconds for a person of shorter duration time,although such a duration time varies depending upon individuals. Thus,in order to complete a procedure from the initiation of the compensationof the wavefront aberration to the photographing within seconds, it isimportant that an optical system reach the aimed wavefront aberrationwith the minimum possible number of times of the compensation.

Additionally, in a field of photographing a retina of an eye forexample, there has been a demand for photographing a sharp image at ahigh-magnification, such that a confirmation is possible to the extentof a visual cell of the retina, in order to increase accuracy inexamination. To meet this demand, since the magnification can be madehigher while sharpness of the image is maintained as the residualaberration becomes smaller, it is necessary to improve a limit of theaberration compensation by using the deformable mirror in which thenumber of electrodes, to which a voltage is applied, is large.

Therefore, in the compensation control of the deformable mirror, how toanticipate the voltage patterns for generating a configuration tocompensate the wavefront aberration remains as a problem which stillcannot be solved, in order for the optical system to reach the aimedwavefront aberration with the minimum possible number of times of thecompensation from data on a shape of the aberration measured by awavefront sensor, even when the deformable mirror having the largenumber of electrodes is used.

SUMMARY

At least one objective of the present invention is to provide awavefront aberration compensating apparatus and an ophthalmologic unithaving the same, capable of accomplishing compensation which suppressesa residual aberration to be small with good responsiveness at a shorttime, and of obtaining an extremely sharp image even ifhigh-magnification is set, even when a deformable mirror having thelarge number of electrodes to which a voltage is applied is used forcompensation of a wavefront aberration.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, theinvention provides a wavefront aberration compensating apparatus,comprising: a deformable mirror which compensates a wavefront aberrationof a light flux entered, the deformable mirror including a plurality ofelectrodes, and a thin-film mirror which changes a configuration thereofin accordance with a voltage value applied to each of the electrodes; anoptical system provided with the deformable mirror, and including anobject subjected to aberration compensation; a wavefront sensor whichreceives the light flux traveled through the object and the deformablemirror, and which measures the wavefront aberration of the light flux; amemory which stores therein a voltage template provided for eachexpansion mode according to a polynomial of wavefront aberration, as avoltage alignment data for the electrodes which induces thecorresponding expansion mode of the expansion modes; and a controllerconfigured to determine a superposition amplitude value of each of theexpansion modes and calculate the voltage value applied to each of theelectrodes by using the voltage templates stored in the memory, suchthat the wavefront aberration obtained by the wavefront sensor becomes adesired aberration, and to repeat compensation of the configuration ofthe thin-film mirror of the deformable mirror on the basis of thecalculated voltage value, such that the wavefront aberration of thelight flux measured by the wavefront sensor is suppressed.

Advantageously, the controller is configured to: apply an initialvoltage to each of the electrodes such that an displacement amount ofthe thin-film mirror becomes an initial displacement amount; and controlthe configuration of the thin-film mirror created according to a voltagepattern generated for the electrodes to be a configuration which negatesa configuration of the wavefront aberration of the light flux enteredthrough the object, such that the wavefront aberration included in thelight flux after reflection from the deformable mirror is suppressed tobe small.

Advantageously, the wavefront sensor comprises: a Hartmann plate inwhich micro-lenses are aligned in a lattice-like configuration; and atwo-dimensional charge-coupled device, and wherein the wavefront sensormeasures the wavefront aberration of the object by: dividing lightreflected from the object according to projection of a point lightsource onto the object and traveled through the object and thedeformable mirror into plural light fluxes by the Hartmann plate;measuring point-image positions of the respective light fluxes by thetwo-dimensional charge-coupled device; and comparing the measuredpoint-image positions with point-image positions according to an idealobject in which the aberration compensation is unnecessary.

Advantageously, the memory stores therein the voltage template providedfor each of the expansion modes according to Zernike polynomials of thewavefront aberration, as the voltage alignment data for the electrodeswhich induces the corresponding expansion mode of the expansion modessubjected to the compensation.

Advantageously, the controller is configured to: load an amplitude valuein each of the expansion modes from expansion data according to Zernikepolynomials of a residual aberration which is after the compensation ofthe wavefront aberration; load the voltage value applied to each of theelectrodes as a previous voltage value used in a previous compensationof the wavefront aberration; load the stored voltage templates inducingthe corresponding expansion modes; calculate objective Zernikepolynomial data of the deformable mirror; load previously calculated aline-column in which wavefront configuration data corresponding to therespective voltage templates are aligned; calculate a superpositioncoefficient obtained from the calculated objective Zernike polynomialdata and the loaded line-column as the superposition amplitude value ofeach of the expansion modes; and calculate the voltage value applied toeach of the electrodes in a current compensation, by the voltagetemplates, the calculated superposition coefficient as the superpositionamplitude value, the previous voltage value, and a feedback gain.

Advantageously, the controller is configured to: load an amplitude valuein each of the expansion modes from expansion data according to Zernikepolynomials of a residual aberration which is after the compensation ofthe wavefront aberration; load the voltage value applied to each of theelectrodes as a previous voltage value used in a previous compensationof the wavefront aberration; load the stored voltage templates inducingthe corresponding expansion modes; calculate a ratio of wavefrontconfiguration data corresponding to the respective voltage templates towavefront configuration data of the respective expansion modes as thesuperposition amplitude value of each of the expansion modes; andcalculate the voltage value applied to each of the electrodes, by thevoltage templates, the calculated ratio as the superposition amplitudevalue, the previous voltage value, and a feedback gain.

Advantageously, the controller is configured to: load an amplitude valuein each of the expansion modes from expansion data according to Zernikepolynomials of a residual aberration which is after the compensation ofthe wavefront aberration; load the voltage value applied to each of theelectrodes as a previous voltage value used in a previous compensationof the wavefront aberration; load the stored voltage templates inducingthe corresponding expansion modes; calculate a value obtained byreversing plus and minus signs of the amplitude value in each of theexpansion modes as the superposition amplitude value of each of theexpansion modes; and calculate the voltage value applied to each of theelectrodes, by the voltage templates, the calculated value as thesuperposition amplitude value, the previous voltage value, and afeedback gain.

Advantageously, the controller is configured to repeat the compensationof the configuration of the thin-film mirror of the deformable mirror,until a residual aberration after the compensation of the wavefrontaberration becomes equal to or less than a target value determined onthe basis of an allowable wavefront aberration in which a sharp image atthe time when at least one of observation and photographing of theobject is obtained by a set magnification.

Advantageously, the object comprises an eye, and wherein the controlleris configured to: perform compensation of a spherical diopter powercomponent and an astigmatism power component within the wavefrontaberration generated due to a flexing characteristic of the eye as alower order wavefront aberration compensation; and compensate acomponent of the wavefront aberration remained after the lower orderwavefront aberration compensation and a component of the wavefrontaberration higher in order than orders subjected to the lower orderwavefront aberration compensation by deforming the deformable mirror.

Advantageously, the controller is configured to: adjust the sphericaldiopter power component within the wavefront aberration by a focusingmechanism of an autofocusing system, on the basis of the measurement ofthe wavefront aberration by the wavefront sensor; adjust the astigmatismpower component within the wavefront aberration by a lens forastigmatism compensation, on the basis of the measurement of thewavefront aberration by the wavefront sensor; and repeat the lower orderwavefront aberration compensation by the adjustment of the sphericaldiopter power component with the focusing mechanism and the adjustmentof the astigmatism power component with the lens, until a residualaberration after the compensation of the wavefront aberration becomesequal to or less than a defined value determined on the basis of secondorder in the expansion modes according to Zernike polynomials.

Advantageously, the controller is configured to: initiate thecompensation of the configuration of the thin-film mirror of thedeformable mirror after the lower order wavefront aberrationcompensation is performed; and repeat the compensation of theconfiguration of the thin-film mirror of the deformable mirror, until aresidual aberration after the compensation of the wavefront aberrationbecomes equal to or less than a target value determined on the basis oforders in the expansion modes by Zernike polynomials, at least to thesixth order.

Advantageously, the controller is configured to perform at least one ofobservation and photographing of a retina of an eye as the object, whena residual aberration after the wavefront aberration becomes equal to orless than a target value.

In addition, the invention provides a wavefront aberration compensatingapparatus, comprising: a deformable mirror which compensates a wavefrontaberration of a light flux entered, the deformable mirror including aplurality of electrodes, and a thin-film mirror which changes aconfiguration thereof in accordance with a voltage value applied to eachof the electrodes; an optical system provided with the deformablemirror, and including an object subjected to aberration compensation; awavefront sensor which receives the light flux traveled through theobject and the deformable mirror, and which measures the wavefrontaberration of the light flux; voltage template storing means for storingtherein a voltage template provided for each expansion mode according toa polynomial of wavefront aberration, as a voltage alignment data forthe electrodes which induces the corresponding expansion mode of theexpansion modes; voltage calculating means for determining asuperposition amplitude value of each of the expansion modes, andcalculating the voltage value applied to each of the electrodes by usingthe voltage templates stored in the voltage template storing means, suchthat the wavefront aberration obtained by the wavefront sensor becomes adesired aberration; and deformable mirror controlling means forperforming a control of repeating compensation of the configuration ofthe thin-film mirror of the deformable mirror on the basis of thevoltage value calculated by the voltage calculating means, such that thewavefront aberration of the light flux measured by the wavefront sensoris suppressed.

Furthermore, the invention provides an ophthalmologic unit, comprisingthe wavefront aberration compensating apparatus according to any one ofthe wavefront aberration compensating apparatuses described above.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the specification, serve to explain theprinciples of the invention.

FIG. 1 is an overall view illustrating an ophthalmologic unit appliedwith a wavefront aberration compensating apparatus according to a firstembodiment of the invention.

FIG. 2A is a plan view illustrating one example of a deformable mirrorshared by a retina photographing system and a wavefront control systemaccording to the first embodiment.

FIG. 2B is a cross-sectional view taken along an A-A line of FIG. 2A.

FIG. 3 is a cross-sectional view illustrating a thin-film mirror andelectrodes of the deformable mirror.

FIG. 4 is a plan view illustrating an example of arrangement of theelectrodes of the deformable mirror.

FIG. 5 is an explanatory view illustrating a wavefront sensor of aphotographing control system according to the first embodiment.

FIG. 6 is a flowchart illustrating a flow of a control processing forcompensating a wavefront aberration executed by a controller of thewavefront control system according to the first embodiment.

FIG. 7 is a diagram illustrating expansion modes according to zero-orderto 10th order Zernike polynomials.

FIG. 8 illustrates one example of voltage templates in the respectiveexpansion modes used in the wavefront aberration compensating apparatusaccording to the first embodiment.

FIG. 9 is an explanatory view illustrating an operation of thecompensation of the wavefront aberration in the deformable mirror.

FIG. 10 is a diagram illustrating a relation of characteristics betweenthe number of times of repetition of the compensation and a residualaberration in the compensation of the wavefront aberration in which thedeformable mirror is used according to a compensation algorithm of thefirst embodiment.

FIG. 11 is a flowchart illustrating a flow of a control processing forcompensating the wavefront aberration executed by the controller of thewavefront control system according to a second embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts. The scope of the present invention, however, is not limited tothese embodiments. Within the scope of the present invention, anystructure and material described below can be appropriately modified.

First Embodiment

First of all, a structure will be described.

FIG. 1 illustrates an ophthalmologic unit applied with a wavefrontaberration compensating apparatus according to a first embodiment of theinvention. Here, for example, the wavefront aberration compensatingapparatus refers to a system realized by having a function of negating awavefront aberration by a deformable mirror, which may sometimes becalled as a compensation optics system or an adaptive optics system.

Referring to FIG. 1, the ophthalmologic unit according to the firstembodiment includes a retina photographing system and a wavefrontcontrol system. The retina photographing system photographs a retina ofan eye, and the wavefront control system compensates a wavefrontaberration by using a deformable mirror built in the retinaphotographing system.

First, the retina photographing system will be described.

The retina photographing system photographs the retina Ef of the eye E.The retina photographing system includes, for example, a semiconductorlaser light source 1, a beam splitter 2, a variable cylindrical lens (alens for astigmatism compensation) 3, a first lens 4, a first mirror 5,a movable prism (focusing mechanism) 6, a second mirror 7, a second lens8, the deformable mirror 9, a dichroic mirror 10, and a highly-sensitiveCCD (Charge-Coupled Device) camera 11.

Semiconductor laser light emitted from the semiconductor laser lightsource 1 passes through the beam splitter 2 and the variable cylindricallens 3, which can be set at the arbitrary power of astigmatism, and thenenters the eye E to illuminate the retina Ef. In the present embodiment,the semiconductor laser light emitted from the semiconductor laser lightsource 1 has a wavelength of 633 nm, although it is not limited thereto.The light reflected from the retina Ef as reflected light is subjectedto reduction of an influence of the astigmatism with the variablecylindrical lens 3 set according to the power of astigmatism of the eyeE. The reflected light then transmits the beam splitter 2, and enters anautofocusing system. The autofocusing system is structured of the firstlens 4, the first mirror 5, the movable prism 6, the second mirror 7,and the second lens 8. The movable prism 6 of the autofocusing system isdriven in a direction of an arrow illustrated in FIG. 1 corresponding toa spherical diopter power of the eye E to change an optical path lengthso as to reduce an influence of myopia, hyperopia and so forth. A lightflux from the autofocusing system becomes substantially parallel light,which is reflected by the deformable mirror 9. A direction of thereflected parallel light is then changed by the dichroic mirror 10 suchthat the parallel light is incident on the highly-sensitive CCD camera11 used for the photographing of the retina. Thereby, the retina isimaged on a coupled device of the highly-sensitive CCD camera 11.

Next, the wavefront control system will be described.

The wavefront control system compensates the wavefront aberration byusing the deformable mirror 9 included in the retina photographingsystem. The wavefront control system includes, for example, asemiconductor laser light source 12, a beam splitter 13, a wavefrontsensor 14, a controller 15, and a driver 16. The semiconductor laserlight source 12 may be replaced by a SLD (Super Luminescent Diode) lightsource. In the present embodiment, a personal computer is used as thecontroller 15, although it is not limited thereto. The controller 15 canbe any device as long as a suitable controlling element, such as a CPU(Central Processing Unit), is included. Note that the wavefront controlsystem according to the present embodiment employs a structure in whichthe deformable mirror 9 of the retina photographing system is sharedtherewith.

Semiconductor laser light emitted from the semiconductor laser lightsource 12 is reflected by the beam splitter 13. In the presentembodiment, the semiconductor laser light emitted from the semiconductorlaser light source 12 has a wavelength of 840 nm, although it is notlimited thereto. The reflected semiconductor laser light then passesthrough the dichroic mirror 10, the deformable mirror 9, theautofocusing system, the beam splitter 2, and the variable cylindricallens 3 to be incident on the eye E, so as to image the retina Ef. Thelight reflected from the retina Ef as reflected light passes through thevariable cylindrical lens 3, the beam splitter 2, and the autofocusingsystem, which is then reflected by the deformable mirror 9 in which aconfiguration thereof is controlled. Thereby, the wavefront aberrationis compensated. Thereafter, the reflected light transmits the dichroicmirror 10 and the beam splitter 13 with a state in which the wavefrontaberration which has not been compensated completely by the deformablemirror 9 is included, i.e., a state that a residual aberration, in whichan aimed aberration is subtracted from the aberration of a light fluxreflected from the deformable mirror 9, is included. Then, reflectedlight, having transmitted the dichroic mirror 10 and the beam splitter13, is incident on the wavefront sensor 14. The wavefront sensor 14includes, for example, a Hartmann plate 14 a and a two-dimensional CCD(Charge-Coupled Device) 14 b. Thereby, information on the wavefrontaberration is detected as an image. The CCD image obtained by thetwo-dimensional CCD 14 b is subjected to an image processing by thecontroller 15, so as to calculate the residual aberration. Thecontroller 15 computes voltage data, used for compensating theconfiguration of a thin-film mirror of the deformable mirror 9, byutilizing a later-described compensation algorithm, and repeats acompensation processing driven by the driver 16 until the calculatedresidual aberration becomes equal to or less than a target value.

The wavefront control system is based on a closed-loop, and iscontrolled such that the residual aberration becomes small. In thepresent embodiment, the retina Ef is photographed at high magnificationby the highly-sensitive CCD camera 11 of the retina photographingsystem, at the time when the residual aberration is decreased to beequal to or less than the target value.

Now, a structure of the deformable mirror 9 will be described.

FIG. 2A illustrates one example of the deformable mirror 9 shared by theretina photographing system and the wavefront control system accordingto the present embodiment. FIG. 2B is a cross-sectional view taken alongan A-A line of FIG. 2A. FIG. 3 is a cross-sectional view whichillustrates the thin-film mirror and electrodes of the deformable mirror9. FIG. 4 illustrates an example of arrangement of the electrodes of thedeformable mirror 9.

Referring to FIGS. 2A and 2B, the deformable mirror 9 includes, forexample, a mirror frame 9 a, a thin-film mirror 9 b, spacers 9 c, anelectrode substrate 9 d, and electrodes 9 e.

Referring to FIG. 3, the thin-film mirror 9 b is stretched on the mirrorframe 9 a, and includes a two-layer structure of a mirror or preferablyan aluminum (Al) mirror 91 disposed on an optical path side, and athin-film or preferably a silicon (Si) thin-film 92 disposed on anelectrode side. The mirror 91 is a reflective film, and formed byevaporating a material having high reflectivity on the thin-film 92. Thethin-film 92 has flexibility, and has a thickness of about 4 μm,although it is not limited thereto.

Each of the spacers 9 c retains a gap length between the thin-filmmirror 9 b and the electrodes 9 e at a predetermined value. In thepresent embodiment, a ball having high rigidity is used for the spacers9 c, although it is not limited thereto.

Referring to FIG. 4, for example, the plural electrodes 9 e are disposedon the electrode substrate 9 d, and are divided into 85 electrodes to bealigned concentrically and radially. In FIG. 4, black spots denoteapplication points, and a dashed line denotes an analysis area in whichthe wavefront is regenerated from wavefront measurement data. In thepresent embodiment, the analysis area is set in an area connecting theapplication points located at the outermost circumference of theelectrode substrate 9 d.

Referring to FIG. 2B, the driver 16 is provided as a circuit for drivingthe respective electrodes 9 e, i.e., an electrode 1 to an electrode “n”,individually with voltage. Referring to FIG. 3, electrostatic voltagevalues V₁ to V_(n) are applied to the respective electrodes 9 e, suchthat the deformation of the thin-film mirror 9 b is generatedcorresponding to each of the electrodes 9 e.

Next, a structure of the wavefront sensor 14 will be described.

FIG. 5 illustrates the wavefront sensor 14 of the photographing controlsystem.

Referring to FIG. 5, the wavefront sensor 14 includes, for example, theHartmann plate 14 a in which micro-Fresnel lenses are aligned in alattice-like configuration, and the two-dimensional CCD 14 b disposedparallel to the Hartmann plate 14 a and separated from the Hartmannplate 14 a at a predetermined interval.

The measurement of the wavefront aberration by the wavefront sensor 14 bis performed by projecting a point light source onto the retina Ef or anamphiblestode of the eye E, dividing the reflected light from the retinainto plural light fluxes with the Hartmann plate 14 a, and measuringpoint-image positions of the respective light fluxes by thetwo-dimensional CCD 14 b. Then, by comparing the measured point-imagepositions with point-image positions according to a non-aberration eye,the wavefront aberration appears as an amount of displacement (Δx, Δy)of each point-image. The displacement amounts (Δx, Δy) of the respectivepoint-images correspond to an inclination of a configuration of thewavefront aberration. Thus, the wavefront aberration is restored by thedisplacement amounts. Therefore, it is possible to measure the wavefrontaberration with high accuracy, by setting of the number of the microFresnel lenses aligned in the lattice-like configuration and setting ofthe number of elements of the two-dimensional CCD 14 b.

The wavefront sensor 14 measures an initial wavefront aberration beforethe compensation and the residual aberration in each repetition of thecompensation. A result of the measurement of the initial wavefrontaberration and the residual aberration in each repeated compensation bythe wavefront sensor 14 is used as input information of a compensationalgorithm for a higher order wavefront aberration, which deforms thedeformable mirror 9 into a phase configuration opposite to that of thewavefront. Here, the result of the aberration measurement by thewavefront aberration is used also as input information for compensationof a lower order wavefront aberration, which compensates a sphericaldiopter power component and an astigmatism power component within thewavefront aberration generated due to flexing characteristics of the eyeE.

FIG. 6 is a flowchart illustrating a flow of a control processing forcompensating the wavefront aberration executed by the controller 15 ofthe wavefront control system according to the first embodiment.Hereinafter, each step of the control processing will be described. Thecontrol processing for the compensation of the wavefront aberration isactivated by manipulation by an operator of initiating observation,photographing and so forth of an image of the retina at the highmagnification, for example.

Referring to FIG. 6, in a step S1, an initial voltage V0 is applied toall of the electrodes 9 e of the deformable mirror 9 to performinitialization of the deformable mirror 9. More specifically, thethin-film mirror 9 b of the deformable mirror 9 becomes unstable when avoltage of each of the electrodes 9 e exceeds a voltage V_(p) in whichthe interval between the thin-film mirror 9 b and the electrodes 9 ebecomes ⅔, and thereby the electrodes 9 e and the thin-film mirror 9 bcontact with each other, which may be hereinafter referred to as aphenomenon of pull-in. Therefore, in the present embodiment, the initialvoltage V0 is set at a value slightly lower than that of the voltageV_(p), which causes the pull-in, in a case in which the voltage havingthe same voltage value is applied to all of the electrodes 9 e.Accordingly, an average value of the voltage for the entire electrodesis fixed at the initial voltage V0 in the subsequent control of thedeformable mirror, whereby the pull-in phenomenon is prevented fromoccurring, and a range of control of the voltage is widened, and at thesame time, a fluctuation in the spherical diopter power component (n,m)=(2, 0) is suppressed.

In a step S2, after the initialization of the deformable mirror in thestep S1, the movable prism 6 of the autofocusing system, which correctsthe spherical diopter power component such as myopia, hyperopia and soforth within the wavefront aberration, is moved to an initial positionor a point of origin.

In a step S3, after the movement of the movable prism 6 to the origin inthe step S2, the variable cylindrical lens 3, which corrects theastigmatism power component within the wavefront aberration, is moved toan initial position or a point of origin. It is to be noted that thesteps S1 to S3 correspond to an initialization process.

In a step S4, the wavefront aberration is measured on the basis of asignal supplied from the wavefront sensor 14 with respect to respectiveexpansion modes according to Zernike polynomials, after the movement ofthe variable cylindrical lens 3 to the origin in the step S3, movementof the movable prism 6 and the variable cylindrical lens 3 in a step S6,or an output of voltage values in a step S15.

Hereinafter, the expansion modes according to the Zernike polynomialswill be described.

A difference between the wavefront aberration of the eye E and awavefront aberration to be compensated, i.e., the residual aberration,is expanded by the Zernike polynomials as follows.

W(r,θ)=Σ{A _(m) ×Z _(m)(r,θ)}

where W (r, θ) is the residual aberration, Z_(m) (r, θ) is the Zernikepolynomial of the expansion mode “m”, and A_(m) is an amplitude value ofthe expansion mode according to each of the Zernike polynomials. Here,with reference to FIG. 7, the expansion modes “m” are assigned withnumbers, subsequently from lower order modes, from m=1 to m=M (M is amaximum value of higher order modes), with respect to respective orders“n” (0 to 10) and respective mode forms “m” (−10 to 0 to 10).

In addition, the “respective expansion modes according to the Zernikepolynomials” in the present embodiment refers to modes expanded by eachof the Zernike polynomials when a wavefront aberration is decomposed byZernike polynomials often used in a field of optics. Each of theexpansion modes corresponds to independent shape of wavefront, i.e.,modes. FIG. 7 illustrates each of the expansion modes according to thezero-order to 10th order Zernike polynomials, and each expansion modecorresponds to a classical wavefront aberration. Therefore, it ispossible to know components of the aberration.

In a step S5, after the wavefront measurement and the Zernike expansionin the step S4, whether or not the residual aberration (astigmatismpower component, spherical diopter power component) is equal to or lessthan a defined value is judged.

In the present embodiment, the defined value is determined inconsideration of the 2nd order in the expansion modes according to theZernike polynomials. More specifically, the defined value is determinedbased on the six lower order modes within a frame illustrated in FIG. 7,for example. The 6 lower order modes can be represented by (n, m)=(0,0), (1, −1), (1, 1), (2, −2), (2, 0) and (2, 2), in terms of arelationship between the orders “n” and the mode forms “m”. It is to benoted that zero-order of n=0 is a phase and 1st order is a tilt, whichare irrelevant to a blur of an image.

In the step S5, when the residual aberration is judged not equal to orless than the defined value (No in the step S5), the flow moves to thestep S6, whereas when the residual aberration is judged equal to or lessthan the defined value (Yes in the step S5), the flow moves to a stepS7.

In the step S6, after the judgment as “the residual aberration>thedefined value” in the step S5, the spherical diopter power component((n, m)=(2, 0)) within the wavefront aberration is adjusted by movingthe movable prism 6 of the autofocusing system, and the astigmatismpower component ((n, m)=(2, −2), (2, 2)) within the wavefront aberrationis adjusted by moving the variable cylindrical lens 3.

This compensation of the lower order wavefront aberration adjusts thespherical diopter power component and the astigmatism power componentwithin the wavefront aberration to be decreased. More specifically, thecompensation of the lower order wavefront aberration is performed bymoving the movable prism 6 and the variable cylindrical lens 3 as in acase in which correction is performed with spectacle lenses, contactlenses and so forth, in accordance with a degree of myopia, a degree ofhyperopia, a degree of astigmatism detected by the wavefront sensor 14.

Here, a loop of the compensation of the lower order wavefront aberrationin an order from the step S5, the step S6 and the step S4 is repeateduntil the residual aberration (astigmatism power component, sphericaldiopter power component) is judged to be equal to or less than thedefined value in the step S5.

In a step S7, after the judgment as “the residual aberration(astigmatism power component, spherical diopter power component)≦thedefined value” in the step S5, whether or not the residual aberration isequal to or less than a target value is judged.

In the present embodiment, the target value is determined on the basisof an allowable wavefront aberration in which a sharp image isobtainable when the retina Ef, as an object subjected to the aberrationcompensation, is observed, photographed and so on, by a setmagnification. For example, the target value is determined inconsideration of the orders in the expansion modes by the Zernikepolynomials, at least to the 6th order. In addition, when there is ademand for high magnification, the target value is determined based onthe orders from 6th to 10th in the expansion modes by the Zernikepolynomials, in accordance with the magnification.

More specifically, when, for example, photographing a visual cell of theretina Ef having 2 μm to 5 μm, the wavefront aberration in the analysisarea in a case of the optical system according to the present embodimentis less than 0.05 μm in an actual measurement value of a RMS (Root MeanSquare), in order to observe such a visual cell. Thus, the target valueis determined on the basis of that actual measurement value according tothe RMS.

Here, the RMS is one of indexes of the wavefront aberration, andrepresents a standard deviation or the square root of a variance betweenan ideal wavefront aberration and an actual wavefront aberration.

In the step S7, when the residual aberration is judged not equal to orless than the target value (No in the step S7), the flow moves to thestep S8, whereas when the residual aberration is judged equal to or lessthan the target value (Yes in the step S7), the flow moves to a stepS16.

In a step S8, after the judgment as “the number of times of thecompensation loop≦the set number of times n” in the step S7, theamplitude values (A*=A₁, A₂, . . . , A_(m)) in the respective expansionmodes are loaded from expansion data of the Zernike polynomials of theresidual aberration calculated in the step S4. Hereinafter, the asterisk“*” represents a vector.

In a step S9, after the loading of the amplitude values (A*=A₁, A₂, . .. , A_(m)) in the respective expansion modes in the step S8, the voltagevalues (V*=V₁, V₂, . . . , V_(n)) applied to the respective electrodes 9e at the loading of the amplitude values are loaded.

It is to be noted that the voltage values (V*=V₁, V₂, . . . , V_(n)) areused in the previous control of the electrodes 9 e. The values of theinitial voltage V0 described in the step S1 are used in the initialcontrol.

In a step S10, after the loading of the voltage values (V*=V₁, V₂, . . ., V_(n)) in the step S9, voltage templates Vm* to be used in the currentarithmetic processes are loaded from the previously-stored voltagetemplates Vm* (voltage template storing means), which are determinedfrom a result of experiments. In the present embodiment, the voltagetemplates are stored in a memory included in the controller 15.Alternatively, the voltage templates may be stored in an externalrecording medium, which can be detachably connected or remotelyconnected to the controller 15.

Referring to FIG. 8, for example, the voltage template Vm* is data onalignment of voltage set for each of the expansion modes according tothe Zernike polynomials of the wavefront aberration and which induceseach of the corresponding expansion modes. In addition, the voltagetemplate Vm* is provided for each of the expansion modes from the lowerorder modes to the higher order modes subjected to the compensation(preferably 6th order or higher), excluding the six lower modes (n,m)=(0, 0), (1, −1), (1, 1), (2, −2), (2, 0) and (2, 2) as the modessubjected to the compensation of the lower order wavefront aberration.

In a step S11, after the loading of the voltage templates Vm* in thestep S10, objective Zernike polynomial data Z*_(target) as the objectiveconfiguration generated by the deformable mirror 9 are calculated byusing Z*_(target)=(Zt₁, Zt₂, Zt₃, Zt₄, . . . , Zt_(m)).

More specifically, the residual aberration of the light flux havingpassed through the deformable mirror 9 is represented as:

A*+Z*_(target)

Therefore, when the deformable mirror 9 is to be controlled such thatthe residual aberration of the light flux having passed through thedeformable mirror 9 is eliminated, the following is established.

Z*_(target)=−A*

In a step S12, after the calculation of the objective Zernike polynomialdata Z*_(target) in the deformable mirror 9 in the step S11,line-columns ZM previously calculated are loaded.

Here, the line-columns ZM are amplitude vector data of the actualwavefront aberration generated when the voltages of the voltagetemplates V_(m)* inducing the particular Zernike expansion mode “m” areapplied to the electrodes 9 e, which are arranged in a matrix form anddetermined by a result of experiments. Thereby, ideally, only a singleZernike expansion mode should be generated, although actually, otherZernike expansions mores are mixed, due to imperfection of thetemplates. Due to such imperfection of the templates, the line-columnsZM are set.

As described above, the line-columns ZM are defined by a followingformula.

${ZM} = \begin{pmatrix}Z_{1,1} & Z_{2,1} & \cdots & Z_{m,1} \\Z_{1,2} & Z_{2,2} & \; & Z_{m,2} \\\vdots & \; & \; & \vdots \\Z_{1,m} & Z_{2,m} & \cdots & Z_{m,m}\end{pmatrix}$

Alternatively, in order to speed up the calculation by simplification,the line columns ZM may also be defined by a following formula (1).

$\begin{matrix}{{ZM} \approx \begin{pmatrix}Z_{1,1} & 0 & \cdots & 0 \\0 & Z_{2,2} & \; & 0 \\\vdots & \; & \; & \vdots \\0 & 0 & \cdots & Z_{m,m}\end{pmatrix}} & (1)\end{matrix}$

Alternatively, a flow of the calculation can also be proceeded by afollowing formula (2) in which the voltage templates are normalized, andin which Z_(m,m) is set to be one.

$\begin{matrix}{{ZM} \approx \begin{pmatrix}1 & 0 & \cdots & 0 \\0 & 1 & \; & 0 \\\vdots & \; & ⋰ & \vdots \\0 & 0 & \cdots & 1\end{pmatrix}} & (2)\end{matrix}$

In a step S13, after the loading of the line-columns ZM in the step S12,superposition coefficients k* are calculated from a following formula.

k*=ZM ⁻¹ ·Z* _(target)

This formula is for obtaining such superposition coefficients k* thatthe following is established.

Z* _(target) ≈ZM·k*

Here, in a case of the formula (1) which ignores the imperfection of thetemplates, the following is established.

$k^{*} = ( {\frac{Z_{t\; 1}}{Z_{1,1}}\mspace{20mu} \frac{Z_{t\; 2}}{Z_{2,2}}\mspace{20mu} \cdots \mspace{20mu} \frac{Z_{tm}}{Z_{m,m}}} )$

Therefore, when the deformable mirror 9 is so set that the aberration iseliminated with the deformable mirror 9 in the case of the formula (2),the following is represented.

k*=−A*

In a step S14, after the calculation of the superposition coefficientsk* in the step S13, the square values V_(n) ² of the voltage valuesV_(n) for obtaining a configuration of the thin-film mirror 9 b of thedeformable mirror 9, that eliminates the aberration, are calculated froma following formula, determined since the square of the voltage isvirtually in proportional to the displacement amount.

V _(n) ² =V _(n)′² +gΣ{k _(m) ×V _(mn) ²}

where the V_(n) loaded in the step S9 is replaced by V_(n)′ in theprevious control cycle, and “g” is a feedback gain or a compensationcoefficient determined from experiments, which is changeable for eachorbicular zone or each electrode. The feedback gain “g” is designed at avalue such that no divergence is occurred in the correction of thehigher order wavefront aberration, and that the residual aberrationbecomes equal to or less than the target value with good responsivenessand reduced number of repeated times of the compensation loop.

In the step S15, after the calculation of the square of the voltagevalues in the step S14, the voltage values V_(n) are determined by thesquare voltage values V_(n) ² obtained in the step S14, and drivinginstructions for applying the determined voltage values V_(n) to therespective electrodes 9 e are outputted to the driver 16. The flowreturns to the step S4 after the completion of the step S15, tostructure a compensation loop of the higher order wavefront aberration.

In a step S16, after the judgment as “the residual aberration≦the targetvalue” in the step S7, a photographing mode for carrying out the highmagnification photographing of the retina Ef is performed.

In the flowchart illustrated in FIG. 6, the steps S1 to S6 correspond tolower order wavefront aberration compensating means, the steps S8 to S14correspond to voltage calculating means, and the steps S4, S5, and S7 toS15 correspond to deformable mirror controlling means.

Now, operation according to the present embodiment will be described.

Hereinafter, operation performed by the wavefront aberrationcompensating apparatus according to the present embodiment will bedescribed by sections referred to as “Operation on Compensation Controlof Lower Order Wavefront Aberration”, “Operation on Compensation Controlof Higher Order Wavefront Aberration”, and “Operation on Compensation ofWavefront Aberration by the use of Deformable Mirror and CompensationAlgorithm according to the First Embodiment”.

[Operation on Compensation Control of Lower Order Wavefront Aberration]

Referring to the flowchart of FIG. 6, the flow moves in an order of thesteps S1, S2, and S3, when the control for the compensation of thewavefront aberration is initiated. More specifically, the initializationprocess in which the initialization of the deformable mirror 9 isperformed in the step S1, the movement of the movable prism 6 to theorigin or to a default position is performed in the step S2, and themovement of the variable cylindrical lens 3 to the origin or to adefault position is performed in the step S3, are carried out.

In the step S1, a reason why the initial voltage V0 is applied to all ofthe electrodes 9 e to perform the initialization of the deformablemirror 9 with a state of displacement of the deformable mirror 9 closerto an amount of initial displacement of the deformable mirror 9, is toincrease responsiveness for the convergence toward the objectivewavefront aberration while suppressing hunting in control, by employinga mode of deformation of the deformable mirror 9 in which only adirection in which the pulling force of the thin-film mirror 9 b by theelectrodes 9 e is decreased, in the later-described compensation of thewavefront aberration utilizing the deformable mirror 9.

After the step S3, the flow moves in an order of the steps S4 and S5.The flow in an order of the steps S5, S6, and S4 is repeated until thejudgment as “the residual aberration≦the defined value” is establishedin the step S5.

More specifically, when the judgment “the residual aberration>thedefined value” is established in the step S5, the flow of adjusting thespherical diopter component in the wavefront aberration by moving themovable prism 6 of the autofocusing system and of adjusting theastigmatism power component in the wavefront aberration by moving thevariable cylindrical lens 3 in the step S6, and of measuring thewavefront aberration after the adjustment in the step S4, is repeated.

When the judgment as “the residual aberration≦the defined value” isestablished in the step S5, the loop of compensation of the lower orderwavefront aberration, in which the flow of proceeding in the order ofthe steps S5, S6, and S4 is repeated, is finished, and the flow moves onto the process of compensating the higher order wavefront aberration inand after of the step S7.

Accordingly, in the embodiment of the invention, the compensation loopfor the lower order wavefront aberration including the steps S4, S5, andS6, which compensates the spherical diopter component and theastigmatism power component in the wavefront aberration generated due tothe flexing characteristics of the eye E, is provided. Thus, in thelater-described compensation loop for the higher order wavefrontaberration, a wavefront aberration component remained after thecompensation of the lower order wavefront aberration by the compensationloop for the lower order wavefront aberration, and a wavefrontaberration component higher in order than the orders subjected to thelower order wavefront aberration compensation, are compensated bydeforming the deformable mirror 9.

Therefore, a burden in the compensation of the wavefront aberration inthe compensation loop for the higher order wavefront aberration isreduced significantly. Hence, it is possible to increase theresponsiveness for the convergence of the residual aberration to beequal to or less than the target value, and to reduce the number oftimes of the repetition of the compensation in the compensation loop forthe higher order wavefront aberration.

[Operation on Compensation Control of Higher Order Wavefront Aberration]

Referring to FIG. 6, when the judgment as “the residual aberration(astigmatism power, spherical diopter power)≦the defined value” isestablished in the step S5, the flow proceeds in an order of the stepsfrom the step S5 to S7, S8, S9, S10, S11, S12, S13, S14, and S15.

More specifically, in the step S8, the amplitude values (A*=A₁, A₂, . .. , A_(m)) in the respective modes are loaded from the expansion data ofthe Zernike polynomials of the residual aberration. Then, in the stepS9, the voltage values (V*=V₁, V₂, . . . , V_(n)) applied to therespective electrodes 9 e at the time of the loading of the amplitudevalues are loaded. In the step S10, the voltage templates V_(m)*corresponding to the Zernike polynomial mode “m” to be compensated inthe current occasion are loaded. Thereafter, in the step S11, theobjective Zernike polynomial data Z*_(target) are calculated from theformula: Z*_(target)=(Zt₁, Zt₂, Zt₃, Zt₄, . . . , Zt_(m)). In the stepS12, the previously-calculated line-columns ZM are loaded, and in thestep S13, the superposition coefficients k* are calculated. In the stepS14, the square values V_(n) ² of the voltage values V_(n) for obtainingthe objective mirror deformation are calculated. In the step S15, thevoltage values V_(n) are determined by the square voltage values V², anddriving instructions for applying the determined voltage values V_(n) tothe respective electrodes 9 e are outputted to the driver 16.

The flow returns to the step S4 after the output of the voltage valuesin the step S15. In the step S4, the wavefront aberration after theoutput of the voltage values V_(n), determined in the current arithmeticprocesses, to the respective electrodes 9 e is measured. Then, the flowproceeds in the order of steps S5 and S7. Thereafter, the flow whichproceeds in an order of the steps S8, S9, S10, S11, S12, S13, S14, S15,S4, S5, and S7 in the flowchart of FIG. 6 is repeated as long as thejudgment as “the residual aberration>the target value” is established inthe step S7. In other words, a compensation loop of the higher orderwavefront aberration is structured during when the judgment as “theresidual aberration>the target value” is established.

When the judgment as “the residual aberration≦the target value” isestablished in the step S7, the flow proceeds from the step S7 to thestep S16. In the step S16, the flow moves on to the photographing modein which the high magnification photographing of the retina Ef iscarried out.

Therefore, according to the wavefront aberration compensating apparatusof the first embodiment, the superposition coefficients k* of therespective expansion modes are calculated, and the voltage values V_(n)to be applied to the electrodes 9 e are calculated from the storedvoltage templates V_(m)* such that the wavefront aberration obtained bythe wavefront sensor 14 becomes a desired aberration, in the steps S8 toS14. In the compensation loop of the higher order wavefront aberration,the control in which the compensation for the configuration of thethin-film mirror of the deformable mirror 9 is repeated is performed onthe basis of the calculated voltage values V_(n), such that thewavefront aberration of the light flux measured by the wavefront sensoris suppressed.

Operation on Compensation of Wavefront Aberration By the Use ofDeformable Mirror and Compensation Algorithm According to the FirstEmbodiment

First, a structure of the deformable mirror 9 and a calculation methodfor the control voltages of the deformable mirror 9 will be described.

The electrodes 9 e are arranged to face the grounded conductivethin-film mirror 9 b in the deformable mirror 9. The thin-film mirror 9b of the deformable mirror 9 is distorted due to an electrostatic forceby application of the voltage to each of the electrodes 9 e. When thevoltages are applied to the respective electrodes located under a partof the thin-film mirror 9 b where a dent or deformation is to be formed,the thin-film mirror 9 b is dented or deformed. Here, an amount of thedent or the deformation is substantially in proportional to square ofthe voltage.

A configuration or a shape generated by the deformable mirror 9 isdetermined by an alignment pattern of the electrodes 9 e, the number ofthe electrodes 9 e, and a level of the voltage applied to each of theelectrodes 9 e. More specifically, a large variety of configurations orshapes of the deformable mirror 9 can be provided when the number of theelectrodes 9 e is increased, although this takes extremely long time tocalculate the voltages. Thus, the diversity of the configurations forthe compensation and a speed of processing have a tradeoff relationship,when the realtime compensation is to be performed.

In addition, the calculation of the control voltages for generating sucha configuration of the deformable mirror 9 which compensates themeasured wavefront aberration is extremely difficult. In particular, thethin-film mirror 9 b is a continuum. Thus, when the voltage is appliedto one electrode, not only a part of the thin-film mirror in thevicinity of the voltage deforms but the entire surface of the mirror isinfluenced thereby. Therefore, in a conventional technology, a method inwhich a configuration of an entire surface of a mirror at the time whenone voltage is applied is previously recorded, and in which the voltagefor each of the electrodes is so determined that superposition of theconfigurations of the entire surfaces becomes nearest to an objectiveconfiguration, is employed.

According to the wavefront aberration compensating apparatus of thefirst embodiment, the deformable mirror 9 has the extremely large numberof electrodes 9 e, i.e., a total of 85 electrodes 9 e, as illustrated inFIG. 4. Therefore, since the time required by the conventionalcalculation method of the driving voltages is long, a simplified method,i.e., the compensation algorithm, which calculates the driving voltagesat high speed is expanded according to the present embodiment.

First, a conventional compensation algorithm in which a voltage templateis provided for each electrode will be described.

A following formula is previously provided as a voltage alignment(hereinafter also referred to as a voltage template) which applies avoltage only to one electrode “n”.

V₁^(*) = (V  0  0  ⋯  0  0)         ⋮V_(i)^(*) = (0  ⋯  V  ⋯  0  0)         ⋮V_(n)^(*) = (0  0  0  ⋯  0  V)

In addition thereto, a data array Z_(n)* of a wavefront configuration ina case when the voltage template V_(n)* is applied is previouslyrecorded per number of electrodes. Normally, amplitude data of eachexpansion mode “m” is utilized as data of the data array Z_(n)*, byexpanding wavefront data with Zernike polynomials. Accordingly,description will be made on the basis of the amplitude data Z_(n,m)expanded by the Zernike polynomials. Note that the Z_(n,m) can be basedon other polynomial expansion, actual data on displacement of measuringpoint, and so on.

When the wavefront data Z_(n)* for each of the voltage templates V_(n)*in the case in which only one electrode is driven is referred to asinfluence vectors, the influence vectors Z_(n)* are represented asfollows.

Z₁^(*) = (Z_(1, 1)  Z_(1, 2)  Z_(1, 3)  Z_(1, 4)  ⋯  Z_(1, m))         ⋮Z_(i)^(*) = (Z_(i, 1)  Z_(i, 2)  Z_(i, 3)  Z_(i, 4)  ⋯  Z_(i, m))        ⋮Z_(n)^(*) = (Z_(n, 1)  Z_(n, 2)  Z_(n, 3)  Z_(n, 4)  ⋯  Z_(n, m))

Additionally, when such influence vectors Z_(n)* arranged per number ofthe voltage templates are referred to as influence line-columns ZM, theinfluence line-column ZM are represented as follows.

${ZM} = \begin{pmatrix}Z_{1,1} & Z_{2,1} & \cdots & Z_{n,1} \\Z_{1,2} & Z_{2,2} & \; & Z_{n,2} \\\vdots & \; & \; & \vdots \\Z_{1,m} & Z_{2,m} & \cdots & Z_{n,m}\end{pmatrix}$

Moreover, when the objective configuration generated by the deformablemirror is represented by:

Z*_(target)=(Zt₁, Zt₂, Zt₃, Zt₄, . . . , Zt_(m)), such a value in whicha linear combination of an influence function becomes nearer to theobjective configuration is to be obtained.

When superposition coefficients at the time of the linear combinationare represented by:

k*=(k₁, k₂, . . . , k_(n)), a following formula is established.

$Z_{target}^{*} \approx {{ZM} \cdot {k^{*}\begin{pmatrix}z_{t\; 1} \\z_{t\; 2} \\\vdots \\z_{tm}\end{pmatrix}}} \approx {\begin{pmatrix}Z_{1,1} & Z_{2,1} & \cdots & Z_{n,1} \\Z_{1,2} & Z_{2,2} & \; & Z_{n,2} \\\vdots & \; & \; & \vdots \\Z_{1,m} & Z_{2,m} & \cdots & Z_{n,m}\end{pmatrix} \cdot \begin{pmatrix}k_{1} \\k_{2} \\\vdots \\k_{n}\end{pmatrix}}$

Such superposition coefficients “k*” in which an error between a resultof calculation in a right side and a result of calculation on a leftside becomes the least in the above formula are to be obtained. By usingthe value of the obtained superposition coefficients “k*” to actuallysuperpose the voltage templates, so as to obtain compensation voltagesV*. The superposition of the voltage templates is carried out inconsideration of a displacement which is in proportional to square of avoltage.

$\begin{pmatrix}V_{1}^{2} \\V_{2}^{2} \\\vdots \\V_{n}^{2}\end{pmatrix} = {\begin{pmatrix}V^{2} & 0 & \cdots & 0 \\0 & V^{2} & \; & 0 \\\vdots & \; & \; & \vdots \\0 & 0 & \cdots & V^{2}\end{pmatrix} \cdot \begin{pmatrix}k_{1} \\k_{2} \\\vdots \\k_{n}\end{pmatrix}}$

The foregoing is the calculation of the voltage for the aberrationcompensation by the conventional compensation algorithm in which thevoltage template is provided for each of the electrodes.

What takes time in the conventional calculation is the working-out ofthe superposition coefficients k*, and a problem is that it takesextremely long time when the number of the electrodes “n” is increased.Thus, it is crucial if the number of the electrodes is large in a casein which realtime control is to be carried out.

Now, a method of voltage calculation according to the present embodimentwill be described.

In the present embodiment, the voltage template V_(m)* which induces theparticular Zernike expansion mode “m” is used. When the number of theZernike expansion modes subjected to the compensation is “M”, m-piecesof voltage templates V_(m)* are to be generated.

V₁^(*) = (V_(1, 1)  V_(1, 2)  ⋯  V_(1, n))V_(m)^(*) = (V_(m, 1)  V_(m, 2)  ⋯  V_(m, n))

Here, wavefront configuration data Z_(m)* (equivalent to theabove-described influence vector) corresponding to each of the voltagetemplates V_(m)* and the line-columns ZM, in which the wavefrontconfiguration data Z_(m)* are aligned, are defined as follows.

Z₁^(*) = (Z_(1, 1)  Z_(1, 2)  ⋯  Z_(1, m))         ⋮Z_(m)^(*) = (Z_(m, 1)  Z_(m, 2)  ⋯  Z_(m, m))${ZM} = \begin{pmatrix}Z_{1,1} & Z_{2,1} & \cdots & Z_{m,1} \\Z_{1,2} & Z_{2,2} & \; & Z_{m,2} \\\vdots & \; & \; & \vdots \\Z_{1,m} & Z_{2,m} & \cdots & Z_{m,m}\end{pmatrix}$

In addition, the superposition coefficients k* are determined by thenumber of the voltage templates V_(m)*. Thus, in the present embodimentof the invention, the number of elements is not the n-pieces (the numberof electrodes) but the m-pieces (the number of expansion modes subjectedto compensation).

Therefore, an amount of calculation in a case of obtaining thesuperposition coefficients k* by a formula:

Z*_(target)≈ZM·k* is determined not by the number of electrodes “n” butthe number of the expansion modes “m” subjected to the compensation.Hence, it is possible to reduce the calculation time significantly whena device having the large number of electrodes is used for thedeformable mirror 9.

Additionally, components other than a major component of the wavefrontconfiguration data for each of the expansion modes can be ignored. Afollowing formula is represented when those components are approximatelyignored.

Z₁^(*) ≈ (Z_(1, 1)  0  ⋯  0) Z₂^(*) ≈ (0  Z_(2, 2)  ⋯  0)       ⋮ Z_(m)^(*) ≈ (0  0  ⋯  Z_(m, m))

Thus, the influence line-columns ZM are represented by a followingformula.

${ZM} \approx \begin{pmatrix}Z_{1,1} & 0 & \cdots & 0 \\0 & Z_{2,2} & \; & 0 \\\vdots & \; & \; & \vdots \\0 & 0 & \cdots & Z_{m,m}\end{pmatrix}$

An accuracy in the compensation voltages is decreased when the aboveformula is used, but the superposition coefficients k* are obtainableeasily. Therefore, it is possible to achieve speed-up of the realtimecompensation in which the device having the large number of electrodesis used.

A concrete example will now be described.

(1) Observation of Retina at High Magnification

As one example, in a case of observing the retina Ef at highmagnification, whether or not the observation can be accomplished isdetermined by sharpness or a degree of blur of a photographed image. Thesharpness or the blur is determined by a diffraction limit, whichdepends on an optical system, and by the wavefront aberration. Forexample, when photographing the visual cell of the retina having 2 μm to5 μm, the wavefront aberration in the analysis area in a case of theoptical system according to the present embodiment is less than 0.05 μmin the actual measurement value of the RMS (Root Mean Square), in orderto observe such a visual cell.

(2) The Number of Times of Repeated Compensation

When the retina Ef of the eye E is to be photographed, a duration timein which a person can keep its eye open with good condition is severalseconds for a person of shorter duration time, although such a durationtime varies depending upon individuals. Thus, in order to complete aprocedure from the adjustment to the photographing within seconds, it isimportant to reach the wavefront aberration A according to the aimedwavefront aberration illustrated in FIG. 9 from a state of the wavefrontaberration B illustrated in FIG. 9 with the minimum possible number oftimes of the compensation.

In a case in which the compensation algorithm (the template method foreach expansion mode) of the voltage patterns according to the firstembodiment was employed, the number of times in which a residualaberration saturates, i.e., the number of times in which the residualaberration no longer moves, was 15 times to 50 times, and a reachedvalue of the residual aberration, i.e., a value in which the residualaberration no longer moved, was considerably small. Therefore, it hasfound that an aimed wavefront aberration is reached at the reducednumber of times of the repetition of the compensation.

In an experiment in which the target value of the residual aberrationwas set at 0.05 μm in the actual measurement value of the RMS, aresidual aberration reached a target value by the number of times N ofthe compensation repeated for 5 times to 10 times, as illustrated inFIG. 10. Thereby, the residual aberration of equal to or less than 0.05μm at the RMS, as a condition by which the sharp image is obtainable at22-fold magnification (the magnification set due to an optical system ofan experimental unit), was achieved.

In addition, the residual aberration became equal to or less than thetarget value by the repetition of the compensation repeated about 15times, in an experiment in which the target value of the residualaberration was set less than 0.05 μm in the actual measurement value ofthe RMS. Therefore, the experiments have proved that the wavefrontaberration compensating apparatus according to the present embodiment isan aberration compensation system which satisfies the above (1) and (2).

Second Embodiment

A second embodiment of the invention simplifies a method of calculatingthe superposition amplitude of each of the expansion modes, so as tospeed up the arithmetic processes. Since a system structure of thesecond embodiment is the same or similar to that of the firstembodiment, illustration and description thereon will not be provided indetail.

FIG. 1 is a flowchart illustrating a flow of a control processing forcompensating the wavefront aberration executed by the controller 15 ofthe wavefront control system according to the second embodiment.Hereinafter, each step of the flow will be described. The flowchartillustrated in FIG. 11 omits the steps S11 to S13 of the flowchartillustrated in FIG. 6 according to the first embodiment. In addition,since steps S21 to S31, S35, and S36 of the flowchart illustrated inFIG. 11 perform the same processes as in the steps S1 to S11, S15, andS16 of the flowchart of the FIG. 6, respectively, explanation thereofwill not be given in detail.

In a step S34, after the loading of the voltage templates V_(m)* in thestep S30, the square values V_(n) ² of the voltage values V_(n) forobtaining the configuration of the thin-film mirror 9 b of thedeformable mirror 9, that eliminates the aberration, is calculated froma following formula (3), determined since the square of the voltage isvirtually in proportional to the displacement amount.

V _(n) ² =V _(n)′² +gΣ{(Zt _(m) /Z _(m,m))×V_(mn) ²}  (3)

Alternatively, the above formula (3) may be used to calculate the squarevalues V_(n) ² of the voltage values V_(n), when the simplified formula(1) in which only Z_(mm) are remained and others are set at 0 (zero), isused with respect to the exact definition of the line-columns ZM,according to the description on the step S12 in FIG. 6 according to thefirst embodiment.

In addition, a following formula (4) may be used to calculate the squarevalues V_(n) ² of the voltage values V_(n), when the simplified formula(2) in which the voltage templates are normalized to establish Z_(mm)=1,is used with respect to the formula (1) having simplified the linecolumns ZM, according to the description on the step S12 in FIG. 6.

V _(n) ² =V _(n)′² +gΣ{−A _(m) ×V _(mn) ²}  (4)

Therefore, according to the exemplary embodiment of the inventiondescribed above, the superposition amplitude value of each of theexpansion modes are determined, and the voltage value applied to each ofthe electrodes is calculated by using the stored voltage templates, suchthat the wavefront aberration obtained by the wavefront sensor becomesthe desired aberration. In addition, the control in which thecompensation for the configuration of the thin-film mirror of thedeformable mirror is repeated is performed on the basis of thecalculated voltage values, such that the wavefront aberration of thelight flux measured by the wavefront sensor is suppressed.

More specifically, the wavefront measurement data in the analysis areaof the thin-film mirror obtained by the wavefront sensor are representedas amplitude in the respective expansion modes expanded by polynomialsof the wavefront aberrations. On the other hand, the voltage templatesor voltage alignment data for obtaining configurations of the respectiveexpansion modes are provided, which are then superposed to calculate thevoltage alignment data which corresponds to the objective configuration.At this time, the superposition amplitude can be calculated as beingequal to the amplitude in each of the expansion modes.

Thus, the template method for each expansion mode is employed, in whichthe voltage templates, which induce the corresponding expansion modes,are provided for the respective expansion modes of the polynomials ofthe wavefront aberrations, and in which the superposition amplitude arecalculated as being equal to the amplitude of the expansion modes.Therefore, as compared with the conventional template method in whichthe configuration of the entire surface of the mirror at the time whenone voltage is applied is previously recorded and in which the voltagefor each of the electrodes is so determined that superposition of theconfigurations of the entire surfaces becomes nearest to the objectiveconfiguration, the amount of calculation becomes extremely small only ifthe amplitude in each of the expansion modes is obtained. Hence, thetime required for one compensation processing is reduced.

In addition, the number of voltage templates depends on the number ofexpansion modes, without depending on the number of electrodes. Thus,the amount of calculation is significantly reduced even when thedeformable mirror in which the number of electrodes for applying thevoltages is large is used. In other words, the amount of calculationdoes not so increase even when the number of electrodes for applying thevoltages is increased.

Moreover, by using the voltage templates inducing the respectiveexpansion modes, it is possible to perform the compensation control ofthe wavefront aberration having high initial response in which thewavefront aberration becomes nearer to the target value rapidly in theinitial stage of the compensation for the lower order wavefrontaberration.

As described in the foregoing, the embodiment of the invention employsthe compensation algorithm of the voltage patterns according to “thetemplate method for each expansion mode”, by which the deformable mirroris possible to reach the objective configuration in a short time. Hence,it is possible to suppress the residual aberration to be small with goodresponsiveness at the short time, and to obtain the extremely sharpimage even if the high-magnification is set, even when the deformablemirror having the large number of electrodes to which the correspondingvoltage is applied to each of those, is used for the compensation of thewavefront aberration.

In each of the above-described exemplary embodiments of the invention,the deformable mirror 9 includes a total of 85 electrodes 9 e, althoughit is not limited thereto. The deformable mirror 9 may have more than 85electrodes 9 e, or may have less than 85 electrodes 9 e. In other words,the number of the electrodes of the deformable mirror is not limited bythe embodiments, which can be appropriately changed according tomagnification required, a magnitude of the target value of the residualaberration, and so on. In addition, although it is preferable that thealignment pattern of the electrodes be so arranged that the wavefrontaberrations corresponding to the expansion modes according to theZernike polynomials are obtained easily, the alignment pattern of theelectrodes also largely depends on the maximum order of the compensationorders of the wavefront aberrations. Therefore, the alignment pattern ofthe electrodes is not limited to the patterns described in theembodiments.

In each of the embodiments, the movable prism 6 as a prism is used forthe focusing mechanism, although it is not limited thereto. It is to benoted that the focusing mechanism may be a mirror, or other suitableoptical element. Alternatively, the focusing mechanism can be an opticalelement or an optical member having vertically-arranged planar mirrors,mutually.

In each of the embodiments, the compensation for the lower orderwavefront aberration, which compensates the spherical diopter powercomponent and the astigmatism power component generated due to theflexing characteristics of the eye E, is performed, since the objectsubjected to the compensation according to the embodiments is the eye E,although it is not limited thereto. In a case in which an objectsubjected to the compensation is other than the eye E, for example, whenan object is a lens having a high order wavefront aberration provided inan optical path, the wavefront aberration compensation utilizing thedeformable mirror may be immediately carried out without performing thecompensation of the lower order wavefront aberration.

In each of the embodiments, the target value is determined based on theallowable wavefront aberration such that the sharp image of the retinaEf is obtained, since each of the embodiments is on the basis ofwavefront aberration compensating apparatus provided in an opticalsystem of the ophthalmologic unit which performs the observation and thephotographing of the retina. However, the target value may be determinedsuch that a particular aberration is obtained. Thereby, it is alsopossible to cause a model eye to have the particular aberration.

According to each of the above-described embodiments, the wavefrontaberration compensating apparatus is applied to the ophthalmologic unitwhich performs the observation and the photographing of the retina,although it is not limited thereto. It is possible to apply thewavefront aberration compensating apparatus to various devices having anobject, which requires the compensation of the wavefront aberration, inits optical system, other than the ophthalmologic unit. Such devices maybe, for example but not limited to, a display, in particular a head-updisplay, a telescope, in particular an astrometric telescope, a laserirradiating unit, a microscope, an exposure unit, an optical disc (disk)unit, in particular an optical pickup device, a microfabrication unit,and other suitable devices in which a lens is used.

Accordingly, it is possible to achieve the following (1) to (14) fromthe above-described exemplary embodiments of the present invention.

(1) A wavefront aberration compensating apparatus, comprising: adeformable mirror which compensates a wavefront aberration of a lightflux entered, the deformable mirror including a plurality of electrodes,and a thin-film mirror which changes a configuration thereof inaccordance with a voltage value applied to each of the electrodes; anoptical system provided with the deformable mirror, and including anobject subjected to aberration compensation; a wavefront sensor whichreceives the light flux traveled through the object and the deformablemirror, and which measures the wavefront aberration of the light flux; amemory which stores therein a voltage template provided for eachexpansion mode according to a polynomial of wavefront aberration, as avoltage alignment data for the electrodes which induces thecorresponding expansion mode of the expansion modes; and a controllerconfigured to determine a superposition amplitude value of each of theexpansion modes and calculate the voltage value applied to each of theelectrodes by using the voltage templates stored in the memory, suchthat the wavefront aberration obtained by the wavefront sensor becomes adesired aberration, and to repeat compensation of the configuration ofthe thin-film mirror of the deformable mirror on the basis of thecalculated voltage value, such that the wavefront aberration of thelight flux measured by the wavefront sensor is suppressed.

Therefore, it is possible to suppress the residual aberration to besmall with good responsiveness at the short time, and to obtain theextremely sharp image even if the high-magnification is set, even whenthe deformable mirror having the large number of electrodes to which thecorresponding voltage is applied to each of those, is used for thecompensation of the wavefront aberration.

(2) A wavefront aberration compensating apparatus according to (1),wherein the controller is configured to: apply an initial voltage toeach of the electrodes such that an displacement amount of the thin-filmmirror becomes an initial displacement amount; and control theconfiguration of the thin-film mirror created according to a voltagepattern generated for the electrodes to be a configuration which negatesa configuration of the wavefront aberration of the light flux enteredthrough the object, such that the wavefront aberration included in thelight flux after reflection from the deformable mirror is suppressed tobe small.

Therefore, it is possible to perform the control for the compensation ofthe wavefront aberration in which the hunting in the control issuppressed and having the high responsiveness and convergence, in thecompensation control of the wavefront aberration utilizing thedeformable mirror, by performing the initialization process of thedeformable mirror by which the initial displacement amount is givenpreviously and by fixing the average voltage of the electrodes to theinitial voltage. In addition, it is possible to increase a dynamic rangeof the compensation by increasing the initial displacement amount to theextent in which the pull-in does not occur.

(3) A wavefront aberration compensating apparatus according to (1) or(2), wherein the wavefront sensor comprises: a Hartmann plate in whichmicro-lenses are aligned in a lattice-like configuration; and atwo-dimensional charge-coupled device, and wherein the wavefront sensormeasures the wavefront aberration of the object by: dividing lightreflected from the object according to projection of a point lightsource onto the object and traveled through the object and thedeformable mirror into plural light fluxes by the Hartmann plate;measuring point-image positions of the respective light fluxes by thetwo-dimensional charge-coupled device; and comparing the measuredpoint-image positions with point-image positions according to an idealobject in which the aberration compensation is unnecessary.

Therefore, it is possible to satisfy the demand for high accuracy in themeasurement of the wavefront aberration essential when the compensationof the higher order wavefront aberration at high accuracy is to beperformed.

(4) A wavefront aberration compensating apparatus according to any oneof (1) to (3), wherein the memory stores therein the voltage templateprovided for each of the expansion modes according to Zernikepolynomials of the wavefront aberration, as the voltage alignment datafor the electrodes which induces the corresponding expansion mode of theexpansion modes subjected to the compensation.

Therefore, each of the expansion modes expanded by the Zernikepolynomials corresponds to an independent shape or configuration ofwavefront (mode). Hence, by compensating the wavefront aberration byusing the voltage templates subsequently from a lower order of therespective expansion modes, it is possible to effectively converge theresidual aberration to the target value.

(5) A wavefront aberration compensating apparatus according to any oneof (1) to (4), wherein the controller is configured to: load anamplitude value in each of the expansion modes from expansion dataaccording to Zernike polynomials of a residual aberration which is afterthe compensation of the wavefront aberration; load the voltage valueapplied to each of the electrodes as a previous voltage value used in aprevious compensation of the wavefront aberration; load the storedvoltage templates inducing the corresponding expansion modes; calculateobjective Zernike polynomial data of the deformable mirror; loadpreviously calculated a line-column in which wavefront configurationdata corresponding to the respective voltage templates are aligned;calculate a superposition coefficient obtained from the calculatedobjective Zernike polynomial data and the loaded line-column as thesuperposition amplitude value of each of the expansion modes; andcalculate the voltage value applied to each of the electrodes in acurrent compensation, by the voltage templates, the calculatedsuperposition coefficient as the superposition amplitude value, theprevious voltage value, and a feedback gain.

Therefore, the influence of the imperfection of the templates, by whichthe expansion modes other than the single expansion mode which should begenerated in each of the Zernike expansion modes are mixed is corrected.Hence, it is possible to perform the compensation of the higher orderwavefront aberration at high accuracy, in which the influence by theother expansion modes is eliminated.

(6) A wavefront aberration compensating apparatus according to any oneof (1) to (4), wherein the controller is configured to: load anamplitude value in each of the expansion modes from expansion dataaccording to Zernike polynomials of a residual aberration which is afterthe compensation of the wavefront aberration; load the voltage valueapplied to each of the electrodes as a previous voltage value used in aprevious compensation of the wavefront aberration; load the storedvoltage templates inducing the corresponding expansion modes; calculatea ratio of wavefront configuration data corresponding to the respectivevoltage templates to wavefront configuration data of the respectiveexpansion modes as the superposition amplitude value of each of theexpansion modes; and calculate the voltage value applied to each of theelectrodes, by the voltage templates, the calculated ratio as thesuperposition amplitude value, the previous voltage value, and afeedback gain.

Therefore, it is possible to perform the compensation of the higherorder wavefront aberration by increasing the speed of the calculationprocessing, while the accuracy of eliminating the influence by the maincomponent of the templates with respect to the wavefront configurationdata, within the influence of the imperfection of the templates by whichthe expansion modes other than the single expansion mode which should begenerated in each of the Zernike expansion modes are mixed, ismaintained.

(7) A wavefront aberration compensating apparatus according to any oneof (1) to (4), wherein the controller is configured to: load anamplitude value in each of the expansion modes from expansion dataaccording to Zernike polynomials of a residual aberration which is afterthe compensation of the wavefront aberration; load the voltage valueapplied to each of the electrodes as a previous voltage value used in aprevious compensation of the wavefront aberration; load the storedvoltage templates inducing the corresponding expansion modes; calculatea value obtained by reversing plus and minus signs of the amplitudevalue in each of the expansion modes as the superposition amplitudevalue of each of the expansion modes; and calculate the voltage valueapplied to each of the electrodes, by the voltage templates, thecalculated value as the superposition amplitude value, the previousvoltage value, and a feedback gain.

Therefore, it is possible to perform the compensation of the higherorder wavefront aberration by increasing the speed of the calculationprocessing significantly, by normalizing the templates.

(8) A wavefront aberration compensating apparatus according to any oneof (1) to (7), wherein the controller is configured to repeat thecompensation of the configuration of the thin-film mirror of thedeformable mirror, until a residual aberration after the compensation ofthe wavefront aberration becomes equal to or less than a target valuedetermined on the basis of an allowable wavefront aberration in which asharp image at the time when at least one of observation andphotographing of the object is obtained by a set magnification.

Therefore, it is possible to obtain a sharp image when observing andphotographing for example of an object subjected to the compensation ofthe aberration, regardless of magnitude of set magnification.

(9) A wavefront aberration compensating apparatus according to any oneof (1) to (8), wherein the object comprises an eye, and wherein thecontroller is configured to: perform compensation of a spherical diopterpower component and an astigmatism power component within the wavefrontaberration generated due to a flexing characteristic of the eye as alower order wavefront aberration compensation; and compensate acomponent of the wavefront aberration remained after the lower orderwavefront aberration compensation and a component of the wavefrontaberration higher in order than orders subjected to the lower orderwavefront aberration compensation by deforming the deformable mirror.

Therefore, it is possible to reduce the burden in the compensation forthe higher order wavefront aberration performed by deforming thedeformable mirror, in the ophthalmologic unit in which the eye is set asthe object subjected to the aberration compensation.

(10) A wavefront aberration compensating apparatus according to (9),wherein the controller is configured to: adjust the spherical diopterpower component within the wavefront aberration by a focusing mechanismof an autofocusing system, on the basis of the measurement of thewavefront aberration by the wavefront sensor; adjust the astigmatismpower component within the wavefront aberration by a lens forastigmatism compensation, on the basis of the measurement of thewavefront aberration by the wavefront sensor; and repeat the lower orderwavefront aberration compensation by the adjustment of the sphericaldiopter power component with the focusing mechanism and the adjustmentof the astigmatism power component with the lens, until a residualaberration after the compensation of the wavefront aberration becomesequal to or less than a defined value determined on the basis of secondorder in the expansion modes according to Zernike polynomials.

Therefore, it is possible to negate the astigmatism power component andthe spherical diopter power component as the lower order wavefrontaberration at a short time, by utilizing lenses provided in an opticalpath.

(11) A wavefront aberration compensating apparatus according to (9) or(10), wherein the controller is configured to: initiate the compensationof the configuration of the thin-film mirror of the deformable mirrorafter the lower order wavefront aberration compensation is performed;and repeat the compensation of the configuration of the thin-film mirrorof the deformable mirror, until the residual aberration after thecompensation of the wavefront aberration becomes equal to or less than atarget value determined on the basis of the orders in the expansionmodes by the Zernike polynomials, at least to the sixth order.

Therefore, the residual aberration to the 6th order is removed by thecompensation for the higher order wavefront aberration performed bydeforming the deformable mirror, in the ophthalmologic unit in which theeye is set as the object subjected to the aberration compensation.Hence, it is possible to obtain the sharp image of, for example, theretina at high magnification by which the observation to the degree ofthe visual cell is possible. In addition, it is possible to satisfy thedemand for the higher magnification, by determining the target value inconsideration of the orders from the 6th to 10th in the expansion modesaccording to the Zernike polynomials.

(12) A wavefront aberration compensating apparatus according to any oneof (1) to (11), wherein the controller is configured to perform at leastone of observation and photographing of a retina of an eye as theobject, when a residual aberration after the wavefront aberrationbecomes equal to or less than a target value.

Therefore, it is possible to suppress the wavefront aberration to besmall in a short time even when, for example, the eye as a cause of thegeneration of the wavefront aberration is set in an optical system, andto perform the observation, the photographing and so on of the retina ofthe eye with the sharp image at the high magnification.

(13) An ophthalmologic unit, comprising the wavefront aberrationcompensating apparatus according to any one of (1) to (12).

Therefore, it is possible to provide the ophthalmologic unit whichsuppress the residual aberration to be small with good responsiveness atthe short time, and which obtains the extremely sharp image even if thehigh-magnification is set, even when the deformable mirror having thelarge number of electrodes to which the corresponding voltage is appliedto each of those, is used for the compensation of the wavefrontaberration.

(14) A wavefront aberration compensating apparatus, comprising: adeformable mirror which compensates a wavefront aberration of a lightflux entered, the deformable mirror including a plurality of electrodes,and a thin-film mirror which changes a configuration thereof inaccordance with a voltage value applied to each of the electrodes; anoptical system provided with the deformable mirror, and including anobject subjected to aberration compensation; a wavefront sensor whichreceives the light flux traveled through the object and the deformablemirror, and which measures the wavefront aberration of the light flux;voltage template storing means for storing therein a voltage templateprovided for each expansion mode according to a polynomial of wavefrontaberration, as a voltage alignment data for the electrodes which inducesthe corresponding expansion mode of the expansion modes; voltagecalculating means for determining a superposition amplitude value ofeach of the expansion modes, and calculating the voltage value appliedto each of the electrodes by using the voltage templates stored in thevoltage template storing means, such that the wavefront aberrationobtained by the wavefront sensor becomes a desired aberration; anddeformable mirror controlling means for performing a control ofrepeating compensation of the configuration of the thin-film mirror ofthe deformable mirror on the basis of the voltage value calculated bythe voltage calculating means, such that the wavefront aberration of thelight flux measured by the wavefront sensor is suppressed.

Therefore, it is possible to suppress the residual aberration to besmall with good responsiveness at the short time, and to obtain theextremely sharp image even if the high-magnification is set, even whenthe deformable mirror having the large number of electrodes to which thecorresponding voltage is applied to each of those, is used for thecompensation of the wavefront aberration.

Although the present invention has been described in terms of exemplaryembodiments, it is not limited thereto. It should be appreciated thatvariations may be made in the embodiments described by persons skilledin the art without departing from the scope of the present invention asdefined by the following claims. The limitations in the claims are to beinterpreted broadly based on the language employed in the claims and notlimited to examples described in the present specification or during theprosecution of the application, and the examples are to be construed asnon-exclusive. For example, in the present disclosure, the term“preferably”, “preferred” or the like is non-exclusive and means“preferably”, but not limited to. The use of the terms first, second,etc. do not denote any order or importance, but rather the terms first,second, etc. are used to distinguish one element from another. Moreover,no element or component in the present disclosure is intended to bededicated to the public regardless of whether the element or componentis explicitly recited in the following claims.

1. A wavefront aberration compensating apparatus, comprising: adeformable mirror which compensates a wavefront aberration of a lightflux entered, the deformable mirror including a plurality of electrodes,and a thin-film mirror which changes a configuration thereof inaccordance with a voltage value applied to each of the electrodes; anoptical system provided with the deformable mirror, and including anobject subjected to aberration compensation; a wavefront sensor whichreceives the light flux traveled through the object and the deformablemirror, and which measures the wavefront aberration of the light flux; amemory which stores therein a voltage template provided for eachexpansion mode according to a polynomial of wavefront aberration, as avoltage alignment data for the electrodes which induces thecorresponding expansion mode of the expansion modes; and a controllerconfigured to determine a superposition amplitude value of each of theexpansion modes and calculate the voltage value applied to each of theelectrodes by using the voltage templates stored in the memory, suchthat the wavefront aberration obtained by the wavefront sensor becomes adesired aberration, and to repeat compensation of the configuration ofthe thin-film mirror of the deformable mirror on the basis of thecalculated voltage value, such that the wavefront aberration of thelight flux measured by the wavefront sensor is suppressed.
 2. Awavefront aberration compensating apparatus according to claim 1,wherein the controller is configured to: apply an initial voltage toeach of the electrodes such that an displacement amount of the thin-filmmirror becomes an initial displacement amount; and control theconfiguration of the thin-film mirror created according to a voltagepattern generated for the electrodes to be a configuration which negatesa configuration of the wavefront aberration of the light flux enteredthrough the object, such that the wavefront aberration included in thelight flux after reflection from the deformable mirror is suppressed tobe small.
 3. A wavefront aberration compensating apparatus according toclaim 1, wherein the wavefront sensor comprises: a Hartmann plate inwhich micro-lenses are aligned in a lattice-like configuration; and atwo-dimensional charge-coupled device, and wherein the wavefront sensormeasures the wavefront aberration of the object by: dividing lightreflected from the object according to projection of a point lightsource onto the object and traveled through the object and thedeformable mirror into plural light fluxes by the Hartmann plate;measuring point-image positions of the respective light fluxes by thetwo-dimensional charge-coupled device; and comparing the measuredpoint-image positions with point-image positions according to an idealobject in which the aberration compensation is unnecessary.
 4. Awavefront aberration compensating apparatus according to claim 1,wherein the memory stores therein the voltage template provided for eachof the expansion modes according to Zernike polynomials of the wavefrontaberration, as the voltage alignment data for the electrodes whichinduces the corresponding expansion mode of the expansion modessubjected to the compensation.
 5. A wavefront aberration compensatingapparatus according to claim 1, wherein the controller is configured to:load an amplitude value in each of the expansion modes from expansiondata according to Zernike polynomials of a residual aberration which isafter the compensation of the wavefront aberration; load the voltagevalue applied to each of the electrodes as a previous voltage value usedin a previous compensation of the wavefront aberration; load the storedvoltage templates inducing the corresponding expansion modes; calculateobjective Zernike polynomial data of the deformable mirror; loadpreviously calculated a line-column in which wavefront configurationdata corresponding to the respective voltage templates are aligned;calculate a superposition coefficient obtained from the calculatedobjective Zernike polynomial data and the loaded line-column as thesuperposition amplitude value of each of the expansion modes; andcalculate the voltage value applied to each of the electrodes in acurrent compensation, by the voltage templates, the calculatedsuperposition coefficient as the superposition amplitude value, theprevious voltage value, and a feedback gain.
 6. A wavefront aberrationcompensating apparatus according to claim 1, wherein the controller isconfigured to: load an amplitude value in each of the expansion modesfrom expansion data according to Zernike polynomials of a residualaberration which is after the compensation of the wavefront aberration;load the voltage value applied to each of the electrodes as a previousvoltage value used in a previous compensation of the wavefrontaberration; load the stored voltage templates inducing the correspondingexpansion modes; calculate a ratio of wavefront configuration datacorresponding to the respective voltage templates to wavefrontconfiguration data of the respective expansion modes as thesuperposition amplitude value of each of the expansion modes; andcalculate the voltage value applied to each of the electrodes, by thevoltage templates, the calculated ratio as the superposition amplitudevalue, the previous voltage value, and a feedback gain.
 7. A wavefrontaberration compensating apparatus according to claim 1, wherein thecontroller is configured to: load an amplitude value in each of theexpansion modes from expansion data according to Zernike polynomials ofa residual aberration which is after the compensation of the wavefrontaberration; load the voltage value applied to each of the electrodes asa previous voltage value used in a previous compensation of thewavefront aberration; load the stored voltage templates inducing thecorresponding expansion modes; calculate a value obtained by reversingplus and minus signs of the amplitude value in each of the expansionmodes as the superposition amplitude value of each of the expansionmodes; and calculate the voltage value applied to each of theelectrodes, by the voltage templates, the calculated value as thesuperposition amplitude value, the previous voltage value, and afeedback gain.
 8. A wavefront aberration compensating apparatusaccording to claim 1, wherein the controller is configured to repeat thecompensation of the configuration of the thin-film mirror of thedeformable mirror, until a residual aberration after the compensation ofthe wavefront aberration becomes equal to or less than a target valuedetermined on the basis of an allowable wavefront aberration in which asharp image at the time when at least one of observation andphotographing of the object is obtained by a set magnification.
 9. Awavefront aberration compensating apparatus according to claim 1,wherein the object comprises an eye, and wherein the controller isconfigured to: perform compensation of a spherical diopter powercomponent and an astigmatism power component within the wavefrontaberration generated due to a flexing characteristic of the eye as alower order wavefront aberration compensation; and compensate acomponent of the wavefront aberration remained after the lower orderwavefront aberration compensation and a component of the wavefrontaberration higher in order than orders subjected to the lower orderwavefront aberration compensation by deforming the deformable mirror.10. A wavefront aberration compensating apparatus according to claim 9,wherein the controller is configured to: adjust the spherical diopterpower component within the wavefront aberration by a focusing mechanismof an autofocusing system, on the basis of the measurement of thewavefront aberration by the wavefront sensor; adjust the astigmatismpower component within the wavefront aberration by a lens forastigmatism compensation, on the basis of the measurement of thewavefront aberration by the wavefront sensor; and repeat the lower orderwavefront aberration compensation by the adjustment of the sphericaldiopter power component with the focusing mechanism and the adjustmentof the astigmatism power component with the lens, until a residualaberration after the compensation of the wavefront aberration becomesequal to or less than a defined value determined on the basis of secondorder in the expansion modes according to Zernike polynomials.
 11. Awavefront aberration compensating apparatus according to claim 9,wherein the controller is configured to: initiate the compensation ofthe configuration of the thin-film mirror of the deformable mirror afterthe lower order wavefront aberration compensation is performed; andrepeat the compensation of the configuration of the thin-film mirror ofthe deformable mirror, until a residual aberration after thecompensation of the wavefront aberration becomes equal to or less than atarget value determined on the basis of orders in the expansion modes byZernike polynomials, at least to the sixth order.
 12. A wavefrontaberration compensating apparatus according to claim 10, wherein thecontroller is configured to: initiate the compensation of theconfiguration of the thin-film mirror of the deformable mirror after thelower order wavefront aberration compensation is performed; and repeatthe compensation of the configuration of the thin-film mirror of thedeformable mirror, until the residual aberration after the compensationof the wavefront aberration becomes equal to or less than a target valuedetermined on the basis of the orders in the expansion modes by theZernike polynomials, at least to the sixth order.
 13. A wavefrontaberration compensating apparatus according to claim 1, wherein thecontroller is configured to perform at least one of observation andphotographing of a retina of an eye as the object, when a residualaberration after the wavefront aberration becomes equal to or less thana target value.
 14. An ophthalmologic unit, comprising the wavefrontaberration compensating apparatus according to claim
 13. 15. A wavefrontaberration compensating apparatus, comprising: a deformable mirror whichcompensates a wavefront aberration of a light flux entered, thedeformable mirror including a plurality of electrodes, and a thin-filmmirror which changes a configuration thereof in accordance with avoltage value applied to each of the electrodes; an optical systemprovided with the deformable mirror, and including an object subjectedto aberration compensation; a wavefront sensor which receives the lightflux traveled through the object and the deformable mirror, and whichmeasures the wavefront aberration of the light flux; voltage templatestoring means for storing therein a voltage template provided for eachexpansion mode according to a polynomial of wavefront aberration, as avoltage alignment data for the electrodes which induces thecorresponding expansion mode of the expansion modes; voltage calculatingmeans for determining a superposition amplitude value of each of theexpansion modes, and calculating the voltage value applied to each ofthe electrodes by using the voltage templates stored in the voltagetemplate storing means, such that the wavefront aberration obtained bythe wavefront sensor becomes a desired aberration; and deformable mirrorcontrolling means for performing a control of repeating compensation ofthe configuration of the thin-film mirror of the deformable mirror onthe basis of the voltage value calculated by the voltage calculatingmeans, such that the wavefront aberration of the light flux measured bythe wavefront sensor is suppressed.